Density Functional Theory Study of the Structure and Energetics of Negatively Charged Oligopyrroles

Department of Computational and Data Sciences, George Mason University, MS 6A2, Fairfax, VA 22030
International Journal of Quantum Chemistry (Impact Factor: 1.43). 08/2011; 111(10):2295 - 2305. DOI: 10.1002/qua.22659


First-principles calculations are used to investigate the electronic properties of negatively charged n-pyrrole oligomers with n = 2–18. Chains of neutral oligomers are bent, whereas the negatively charged oligomers become almost planar due to accumulation of negative charge at the end monomers. Isomers of short oligomers (n < 6) display negative electron affinity although the corresponding anions are energetically stable. For longer oligomers with n ≥ 6, the electron affinity is small and positive, slowly increasing with oligopyrrole length. Doping of 12-pyrrole with lithium atoms shows that negative oxidation states are possible due to electron transfer from dopant to oligomer at locations close to dopant. These 12-pyrrole regions support extra negative charge and exhibit a local structural change from benzenoid to quinoid structure in the CC backbone conjugation. Comparison between neutral and doped polypyrrole (PPy) indicates that doped polymers displays a substantial depletion of the band gap energy and the appearance of dopant-based bands in the gap for a 50% per monomer doping level. It is predicted that Li-doped PPy is not metallic. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011

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Available from: Estela Blaisten-Barojas, May 14, 2014
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    • "Results closest to experiment [38] [26] are obtained with B3PW91, reproducing the experimental planar structure of pyrrole (Py) with the smallest error of 1.0%. The B3PW91 approach is then adopted, which additionally allows for comparison with our previous studies [23] [24] [25]. The Py molecule is a C 2v planar structure with a strong dipole moment of 1.94D in the direction of the NAH bond and À23.5, À26.8, À34.4D Å for the diagonal elements of the quadrupole matrix. "
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    ABSTRACT: A classical model potential to simulate pyrrole oligomers in condensed phases is developed in this work. The new potential contains ten parameters that are optimized on a database of energy points calculated within the density functional theory approach. Based on this potential the condensed phase of systems composed of pyrrole oligomers with 4 and 12 monomers is studied as a function of system density. The binding energy, end-to-end distance, radius of gyration, vector and orientational order parameters, and pair correlation functions are reported at T=300 K. The mechanical equilibrium density is determined for both systems. The bulk modulus is reported at these densities, showing that systems composed of short oligomers are softer than systems containing longer oligomers. Analysis of pair correlation functions and order parameters indicates that at equilibrium the system of short oligomers has characteristics of a liquid while the system of longer oligomers shows a chain stacking trend.
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    Computational and Theoretical Chemistry 12/2011; 977(s 1–3). DOI:10.1016/j.comptc.2011.09.030 · 1.55 Impact Factor
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